In the field of water pollution, the potential quantity or amount of pollution that a substance may cause is commonly stated in terms of the effect it would have upon the dissolved oxygen in a body of water or aqueous stream. The more dissolved oxygen that would react with the matter to completely oxidize it, the higher its chemical oxygen demand (COD). The higher the COD, the more such matter is regarded as a pollutant because as more dissolved oxygen is consumed in oxidation reactions with oxygen demanding matter, the less there is remaining to support aquatic plant and fish life. Hence, acceptable pollution levels are stated in terms of the COD of the body of water or stream being monitored and the concentrations of bacteria, virus, and other undesirable germs and micro-organisms.
Conventional pollution control technology at present is separated into various categories or stages of treatment known as primary, secondary and tertiary. Primary treatment is initially by means of a relatively inexpensive process which should effectively oxidize and thereby eliminate a relatively large percentage of such compounds. Compounds which are refractory and remain relatively uneffected by the primary treatment are then oxidized by secondary and tertiary treatments which are more expensive per unit of unoxidized compound than the primary treatment, but effectively oxidize the refractory compounds. Thus, a savings is effected without sacrificing overall treatment efficiency by first using a relatively low cost per unit of COD method on the raw, untreated waste steam, and then oxidizing the remaining, refractory compounds with a relatively higher cost but more efficacious method or methods.
One conventional primary treatment well known in the art is comprised of feeding the waste stream into aerated setting ponds where bacteria which feed on the waste products will metabalize the compounds, thereby eliminating much of their COD.
There are several considerations, however, which indicate that this treatment method is less than perfect. The bacteria which feed on and break up the oxygen demanding compounds multiply rapidly but eventually die and then they require dissolved oxygen to oxidize their remains, thus replacing a portion of the oxygen demand that has been used to eliminate them. In order to overcome this problem, as well as safeguard against any adverse health effects a significant amount of such bacteria might cause, it is common practice to kill the bacteria as well as any other undesirable micro-organisms prior to the discharge of the treated aqueous waste by adding chlorine. Though the chlorine will effectively sanitize the discharged aqueous waste, it will also form compounds with various hydrocarbon compounds found in the treated waste stream as well as in the body of water or stream into which the chlorine-treated waste is discharged. Recent laboratory experiments strongly suggest that a wide variety of such chlorinated compounds may cause cancer in humans when taken internally. Furthermore, the foregoing known process is unsuitable for use aboard a naval vessel because space and treatment time requirements are incompatible with the shipboard constraints with respect to these variables.
The wet oxidation process is another primary treatment known in the art, but has an advantage over the previously discussed bacteriological process in that, though it may be used on dry land, it is also acceptable for use aboard a naval vessel. Essentially the process oxidizes the waste compounds by forcing compressed air through heated aqueous waste that is contained in a pressurized vessel, thus facilitating an oxidation reaction between the waste compounds and the oxygen in said compressed air.
However, it has been determined that acetic acid (or acetate), an organic compound, is one of the last residual organic compounds to be oxidized whenever the aqueous waste stream containing human excrement is oxidized. Thus, this primary treatment process as was the case with the one previously discussed herein, is unable to significantly reduce the COD caused by acetic acid when operated at its respective nominal efficiency modes. It is known that the efficiency of the wet oxidation process may be increased by increasing its operating temperature, i.e. the temperature to which the pressurized aqueous waste is heated and maintained, and that operation in such a mode will enable the oxidation of acetic acid to occur. However, the concomitant increase in operating pressure would more than likely require the structural modification of existing facilities, and the construction of a facility possessing the capability to operate at the high efficiency mode would be more expensive than one built to withstand only nominal efficiency operating pressures. In addition, the high efficiency mode is unacceptable for use aboard a naval vessel due to space, weight, and power constraints.
Reverse osmosis may be employed as a secondary treatment to eliminate virtually any refractory organic from an aqueous waste stream. The process involves forcing the waste stream through a semipermeable membrane, said membrane being impermeable to any or all of the refractory organic pollutants. The process will thereby separate the polluting compounds from the waste stream but, though it provides for their collection, their ultimate disposal remains a problem, i.e., the pollutants are not oxidized into non-oxygen demanding compounds such as CO.sub.2 and H.sub.2 O. The membrane will also require periodic cleansing in order to operate efficiently. Standby procedures must also be considered to prevent the discharge of untreated waste in the event that the membrane suffers a rupture from the application of excessive pressure. Thus, time and power requirements, as well as potential maintenance problems, may make this process unattractive for use abroad a naval vessel.
For background purposes, air oxidation or organic compounds is believed to follow the initiation step: EQU O.sub.2 + H:CH.sub.2 - R .fwdarw. .sup.. O.sub.2 H + .CH.sub.2 - R
where R represents a carbon based organic molecule or chain. Acetic acid, ##STR1## is relatively more resistive to this initiation step than other organic compounds, and, therefore, to further oxidation because the inductive effect of the --CO.sub.2 H group makes the initial hydrogen atom abstraction more difficult. In order to accomplish the initiation step, the relatively strong force between the H proton and its electron and the C nucleus caused by the inductive effect must be overcome by an oxidizing agent which has the power to abstract the H atom (H.sup..). It is known to those experienced in the chemical arts that the hydroxyl radical, noted as .sup.. OH, is a more reactive species than O.sub.2. It is also known that .sup.. OH has the requiste chemical reactivity necessary to abstract the H atom from the carbon atom on acetic acid.
It is known that .sup.. OH may be generated by mixing H.sub.2 O.sub.2 with Fenton type reagents such as Fe.sup.2.sup.+ or Cu.sup.2.sup.+, for example:
Fe.sup.2.sup.+ + H.sub.2 O.sub.2 .fwdarw. Fe.sup.3.sup.+ + OH.sup.- + .sup.. OH PA1 Fe.sup.3.sup.+ + H.sub.2 O.sub.2 .fwdarw. Fe.sup.2.sup.+ + H.sup.+ + .sup.. O.sub.2 H PA1 Fe.sup.2.sup.+ + .sup.. OH .fwdarw. Fe.sup.3.sup.+ + OH.sup.- PA1 Ho.sub.2.sup.. .revreaction. o.sub.2.sup.+ + h.sup.+ PA1 fe.sup.3.sup.+ + O.sub.2.sup.- .fwdarw. Fe.sup.2.sup.+ + O.sub.2 PA1 H.sub.2 o.sub.2 + .oh .fwdarw. ho.sub.2.sup.. + h.sub.2 o
Thus, it appears that acetic or virtually any oxygen demanding organic may be oxidized by adding appropriate proportions of H.sub.2 O.sub.2 and a Fenton type reagent. However, other reactions in the decomposition mechanism compete with the organic pollutants for the available active oxidant in the H.sub.2 O.sub.2, and thereby render a portion of the theoretical oxidizing potential of the H.sub.2 O.sub.2 unavailable for oxidizing organic pollutants.
the practical applicability of this last method is significantly limited by the fact that it will function and effectively remove COD only for pH between 3 and 5.
In addition, should the ferrous or ferric ion be used as the metallic ion catalyst, a portion of the metallic ions will eventually form iron oxide, commonly known as rust. It follows that any body of water into which the treated waste stream containing the ferrous or ferric ion is discharged will suffer discoloration from the iron oxide in solution; the surface of any solid object coming into contact with such water and causing the iron oxide to come out solution will also suffer discoloration.